1. Field of the Invention
The present invention relates to a so-called FIMS (Front-Opening Interface Mechanical Standard) system used when transferring a contained object, for example a wafer, held in a transfer container referred to as a pod between semiconductor processing apparatuses in semiconductor production processing, to a contained-object transfer system for transferring the contained object between the semiconductor processing apparatuses, and more specifically to a contained-object (wafer) transfer system including an FIMS system in which a pod referred to as a so-called FOUP (Front-Opening Unified Pod) that is a sealed container for containing the wafer is placed and a cap of the pod is opened/closed to transfer the wafer from/into the pod and a transfer chamber that has a mini-environment connected to the FIMS system and is provided with a robot for transferring the wafer therein.
2. Related Background Art
Semiconductor production processing used to be performed in a so-called clean room whose inside is highly purified for dealing with a semiconductor wafer. However, in view of addressing the increased sizes of wafers and cost cutting for controlling the clean room, in recent years, a method has being employed in which only an inside of a processing apparatus, a pod (container of wafer), and the mini-environment for accommodating a transfer robot that hands over the wafer from the pod to the processing apparatus are kept in a highly purified state.
The pod includes a main unit in a shape of a substantial cubic that has a shelf therein capable of holding a plurality of wafers disposed at a space in parallel and an opening provided on one of surfaces forming outer surfaces out of/into which the wafer is taken/put, and a cap for closing the opening. A pod having the opening not formed on a bottom surface thereof but on one side surface (a surface facing the mini-environment) thereof is generally referred to as the FOUP. The present invention is mainly addressed to structures using the FOUP.
The above-described mini-environment includes a first opening portion facing an opening of the pod, a door closing the first opening portion, an opening portion at a semiconductor processing apparatus provided for the processing apparatus, a transfer robot that enters an inside of the pod through the first opening portion to hold the wafer and passes through the opening portion at the processing apparatus to transfer the wafer to the processing apparatus. A structure forming the mini-environment includes a placing base supporting the pod such that the opening portion of the pod exactly faces a front face of the door.
On an upper surface of the placing base, there is provided a positioning pin that is fixed into a hole for positioning and disposed on a bottom surface of the pod to regulate a placing position of the pod and a clamp unit that is engaged with a clamped portion and disposed on the bottom surface of the pod to secure the pod onto the placing base. In general, the placing base can be moved a predetermined distance forward and backward with respect to the direction of the door. In order to transfer the wafer disposed in the pod into the processing apparatus, the pod is moved until a cap thereof contacts the door with the pod placed on the placing base. After the cap contacts the door, the cap is removed by the door from the opening portion of the pod. By means of these operations, the inside of the pod and the inside of the processing apparatus are in communication via the mini-environment, and sequential transferring operations of the wafers are repeatedly performed. The placing base, door, first opening portion, opening/closing mechanism of the door, wall that is provided with the first opening portion therein and forms a part of the mini-environment are generally referred to the FIMS system.
In general, the inside of the pod containing the wafer is filled with dried nitrogen controlled to be highly purified so that contaminated subjects and oxidation gas are prevented from entering the pod. However, when bringing the wafer disposed in the pod into various processing apparatuses to perform a predetermined processing, the inside of the pod and the insides of the processing apparatuses are always kept connected together. According to Japanese Patent Application Laid-Open No. 2006-019726, a fan and a filter are disposed above a chamber where a transfer robot is provided and purified air including controlled particles is generally fed into the chamber. However, when such air enters the pod, a surface of the wafer can be oxidized by oxygen or moisture in the air.
Along with the decreased sizes of semiconductor elements and enhanced performances thereof, more attention has been put on oxidization by the oxygen entering the pod, which has not been conventionally considered as a serious problem. The oxidation gas described above forms a very thin oxidized film on the surface of the wafer or on various kinds of layers formed on the wafer. An existence of such an oxidized film can make it impossible to ensure desired characteristics of the micro semiconductor element. In order to address the problem, it is considered to inhibit the gas in which oxygen partial pressure is not controlled from entering the pod from the outside thereof. As a more specific method, Japanese Patent Application Laid-Open No. 2003-045933 discusses a structure in which a gas supplying nozzle and a gas sucking nozzle are provided in a region near the opening of the pod in the FIMS system to form an air current film for substantially closing the opening of the pod. The formation of the air current film prevents gas entering from the outside of the pod into the inside thereof.
However, for the so-called mini-environment where the transfer robot is disposed, merely general air in which only dust is controlled through a filter is supplied. Therefore, when the wafer is transferred from or into the pod, the wafer always passes through circumstance in which the oxidation gas is not controlled. This transfer operation is actually performed in a very short time, and has not caused such a serious problem in the current process of producing the semiconductors. However, moisture as a phenomenon of condensation can adhere onto the surface of the wafer even in a short time. Once the moisture adheres, it is difficult to inhibit various kinds of thin films from being oxidized.